JPH0365686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When opening and closing an alternating current circuit, the present invention prevents sparks and reduces inrush current when a switch is turned on by opening and closing the electrical circuit near the zero potential of the alternating current. This relates to an AC zero potential switching circuit for measurement.

That is, the present invention applies a voltage from an AC power supply connected to a load through a main circuit of a bidirectional conduction thyristor through a resistor between a base electrode and an emitter electrode of a transistor, so that the collector current is the same as that of the AC power supply. A control current is supplied as a square wave of the frequency from the collector or emitter to the gate electrode of the bidirectional conduction thyristor by a transformer or capacitor coupling circuit, and the collector voltage of the transistor is supplied from the AC power supply via a switch to a rectifier diode and a resistor. The gist of this is an AC zero-potential switching circuit, which is characterized in that it converts to DC using a smoothing circuit with a time constant that is a fraction of the AC power frequency, and the DC voltage increases from the time the switch is turned on. be.

In Figure 1, the voltage of AC power supply AC is connected to terminal U.
A high voltage is applied to the base electrode of the transistor T through the resistor _R3 . Therefore, the output of the transistor T is always in a saturated state, and a rectangular wave output as shown in FIG. 5B is obtained.

The rectangular wave output from the transistor T is passed through the transformer H so that the voltage waveform on the secondary side thereof is made as shown in FIG.

By applying this voltage to the gate electrode of the bidirectional conduction thyristor K shown in FIG.
It becomes conductive when triggered from the rising point of AC voltage.

When the switch S on the terminal U side in FIG. 1 is closed, the capacitor C is charged from the diode D through the resistor _R1 , and the charging curve becomes a steady voltage after several hertz as shown in FIG. 5D. This time constant is determined by the values of resistors R ₁ , R ₂ and capacitor C.

Since the collector voltage of the transistor T in FIG. 1 becomes a voltage as shown in FIG. 5 (d), its output is initially low and the wave height gradually increases as shown in FIG. 5 (b). Therefore, the differentiated output is also the fifth
As shown in Figure C, the gate voltage of the bidirectional conduction thyristor K increases gradually, and only when the mode gate voltage reaches the trigger level of the bidirectional conduction thyristor K.
becomes conductive, so the current is a half-wave current for the first two hertz, and a full-wave current flows from the third hertz, as shown in FIG. 5(e). However, if the time constant is reduced, the bidirectional conducting thyristor K will work at the same time as the switch is turned on.

The one shown in Figure 2 is basically the same as Figure 1, but since the output of the transistor T is obtained by emitter follow, a bidirectional conduction thyristor K that operates with a small current is used. It is suitable for Capacitor _C2 in the figure is for converting the rectangular wave into a differential waveform.

In this way, both the circuits shown in FIGS. 1 and 2,
When the switch S is closed, it becomes conductive from the rising point of the alternating current, and when the switch S is opened, it becomes non-conductive at the falling point of the alternating current, so that spark discharge can be completely eliminated when the switch S is opened and closed.

An example of circuit constants in FIGS. 1 and 2 is as follows.

The alternating current power supply AC is 100 volts or 200 volts, and the resistor R ₁ is 5 kilo ohms or 10 kilo ohms,
Resistor R ₂ is 50 kilo ohms, resistor R ₃ is 100 kilo ohms or 200 kilo ohms, and capacitor C is 10
~100 microfarads.

Further, Z in the figure is a load resistance, which is, for example, various electric appliances such as a light bulb, an electric heater, and a motor, and is connected to an alternating current power supply AC through a main circuit of a bidirectional conduction thyristor K.

Furthermore, depending on the values of the capacitor C and the resistors R ₁ and R ₂ in FIGS. 1 and 2, the circuit is made conductive at the moment the switch S is closed, and various electrical appliances serving as the load resistance Z are started. is also possible.

The circuit shown in Figure 3 is an emitter-follower type circuit in which a transformer H is coupled to the emitter electrode of the transistor T, and the circuit shown in Figure 4 is a circuit with a resistor _R5 and a capacitor connected to the collector of the transistor T.
This is a circuit that combines _C3 , and an appropriate circuit can be adopted as necessary.

[Brief explanation of drawings]

The figures show embodiments of the present invention. Fig. 1 is a circuit diagram of a system in which a transistor and a bidirectional conduction thyristor are driven by the voltage of a rectifier circuit having a time constant, and Fig. 2 is a circuit diagram of a system in which a transistor and a bidirectional conducting thyristor are driven. FIG. 3 is a circuit diagram in which a transformer is coupled to the emitter follower of a transistor, FIG. 4 is a circuit diagram in which a resistor and a capacitor are coupled to the collector of a transistor, and FIG. 5 is a voltage and current waveform diagram. The symbols in the figure are explained as follows.
AC is alternating current power supply, T is transistor, R is low voltage,
C is a capacitor, H is a transformer, D is a diode, K is a bidirectional conduction thyristor, S is a switch,
Z is load resistance.

Claims (1)

[Claims] 1 The voltage from the AC power supply connected to the load through the main circuit of the bidirectional conduction thyristor is applied between the base electrode and emitter electrode of the transistor through the resistor, and the collector current is converted into a rectangular wave with the same frequency as the AC power supply. , a control current is supplied from the collector or emitter to the gate electrode of the bidirectional conduction thyristor by a transformer or capacitor coupling circuit, and the collector voltage of the transistor is transferred from the AC power supply via a switch to the AC power supply by a rectifier diode and a resistor. An alternating current zero potential switching circuit characterized by converting to direct current using a smoothing circuit with a time constant that is a fraction of the frequency so that the direct current voltage increases from the time the switch is turned on.